The only four stroke you'd fit in there would be some of the new generation Saito's. They are really narrow and light. My 82 in my Wot 4 is the same mounting dimensions as your 46 and 10 grams lighter than a 55AX. Power is much the same as your 46 if you were allowing your 46 to rev to 17000 revs, but who does that.
This is what I've been doing. Mounting a REAL ENGINE to the 'Quickie' (as it is labeled inside) which I bought from the club, as part of the donations by Lindsay recently (see website for other tender items). $30 three-channel model now with a AP 15 in the nose. Flew it for the first time on Friday, from our orchard. Nice and quiet, but not a power house. Not easy to tune, as it doesn't have a low-speed needle. The high-speed needle does affect the low speed, so a compromise is all I can get. Good enough for my boys to train with. Better than a Bixler, as the ESC overheats running at part throttle all the time.
![[Image: SaitoFS82b.jpg]](http://www.kingslynnmodelshop.co.uk/images/SaitoFS82b.jpg)